netfilter: nf_conntrack: Add allow_clash to generic protocol handler

netfilter: nf_conntrack: Add allow_clash to generic protocol handler

The upstream commit, 71d8c47fc653711c41bc3282e5b0e605b3727956
 ("netfilter: conntrack: introduce clash resolution on insertion race"),
sets allow_clash=true in the UDP/UDPLITE protocol handler
but does not set it in the generic protocol handler.

As a result, packets composed of connectionless protocols at each layer,
such as UDP over IP-in-IP, still drop packets due to conflicts during conntrack insertion.

To resolve this, this patch sets allow_clash in the nf_conntrack_l4proto_generic.

Signed-off-by: Yuto Hamaguchi <Hamaguchi.Yuto@da.MitsubishiElectric.co.jp>
Signed-off-by: Florian Westphal <fw@strlen.de>